Bay of Bengal sector variability from recent ocean observations and models
Peter Hacker
University of Hawaii at Manoa
Upper ocean observations, made over the past several years in the Bay of Bengal sector, have begun to provide details on the circulation pathways and related temperature and salinity fields. Results from the World Ocean Ciculation Experiment (WOCE) suggest energetic circulation features varying over a broad range of timescales. Recently, upper ocean observations of velocity, temperature and salinity fields were made during April-June and September 1999 as part of the Joint Air-Sea Monsoon Interaction Experiment (JASMINE) in the Bay of Bengal. The 1999 field work was a collaborative pilot study of air-sea fluxes, convection and the upper ocean response to atmospheric forcing. The ocean component's observational goals were to document: the meridional structure of temperature, salinity and velocity fields, the mixed layer and barrier layer structures, and the upper ocean heat, freshwater and momentum budgets as they vary during active and break periods of the monsoon. The April-June survey was focused near 88E from 5S to 16.5N, and included break periods of light winds and upper ocean warming, and active periods of strong winds, variable rainfall, and upper ocean cooling. The data set documents the Bay of Bengal salinity front near8N, the intraseasonal reversal of near-equatorial currents, the associated changes of the temperature and salinity fields (including mixed and barrier layer structures), and the variability of the air-sea fluxes during the southwest monsoon onset.
The new data significantly expand our observational knowledge in the Bay of Bengal sector during the southwest monsoon period. The data suggest that realistic ocean models need to include salinity as well as temperature, need to have high vertical and horizontal resolution to adequately resolve mixed layer and barrier layer structures effecting SST, and need to be forced by high-frequency winds and fluxes. The WOCE and JASMINE data provide detailed information on the spatial and temporal variability of the upper ocean fields, and are proving to be useful for evaluation of realistic ocean models. At the same time, the realistic ocean models can provide a valuable temporal and spatial context for the ocean observations. A challenge for the future is to use the new data and realistic model runs for the design of future process experiments and monitoring activities.
